Where are foreign keys stored?

Where are foreign keys stored?

child table
Foreign key references are stored within a child table and links up to a primary key in a separate table. The column acting as a foreign key must have a corresponding value in its linked table.

Where is foreign key constraint in DB2?

The foreign key of a DB2 table can be found using SYSIBM. SYSFOREIGNKEYS table and SYSIBM. SYSRELS table. The SYSFOREIGNKEYS is a DB2 system table which contains one row for every column of every foreign key.

What is a foreign key in DB2?

A foreign key is a set of columns in a table which are required to match at least one primary key of a row in another table. It is a referential constraint or referential integrity constraint. It is a logical rule about values in multiple columns in one or more tables.

What is the concept of foreign key?

A foreign key is a column (or combination of columns) in a table whose values must match values of a column in some other table. FOREIGN KEY constraints enforce referential integrity, which essentially says that if column value A refers to column value B, then column value B must exist.

Which table should hold the foreign key?

The table that contains the foreign key is considered the child table, and the table that the foreign key references is the parent table. The foreign key restricts what data can be stored in the foreign key columns in the child table, based on the data in the referenced columns in the parent table.

Where does the foreign key go in one-to-many relationship?

If there is a one-to-many relationship between two entities, add the key of the entity on the “one” side (the parent) into the child table as a foreign key.

What are the mandatory components of DB2?

The complex DB2 internal structure has been divided into 5 major components / Address Spaces:

  • System Services component / System Services Address Space (Job: DSN1MSTR)
  • Locking Services component/ Locking Services Address Space (Job: IRLMPROC)
  • Database Services component/ Database Services Address Space (DSN1DBM1)

Can foreign keys be null in Db2?

A foreign key containing null values cannot match the values of a parent key, since a parent key by definition can have no null values. However, a null foreign key value is always valid, regardless of the value of any of its non-null parts.

How do I add a foreign key in Db2?

To add foreign keys using the Control Center:

  1. Expand the object tree until you see the Tables folder.
  2. Right-click the table you want to modify, and select Alter from the pop-up menu.
  3. On the Keys page, click Add.
  4. Select one or more columns to be foreign keys.

Can we have 2 foreign keys in a table?

A table can have multiple foreign keys based on the requirement.

Why is foreign key used?

The FOREIGN KEY constraint is used to prevent actions that would destroy links between tables. A FOREIGN KEY is a field (or collection of fields) in one table, that refers to the PRIMARY KEY in another table.

Can we have two foreign keys in a table?